Mold part



Patented Nov. 22, 1932v UNITED STATES [PATENT OFFICE- GEORGE H. WEIDEMANN, 0F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN MOLD PART No Drawing.

While the present improvements relate more particularly to the casting of magnesium and so-called light metal alloys in whichmagnesium is the predominant constituent, it will be understood that the improved method and means involved are further adaptable for the casting of other similar readily oxidizable metals. The ditliculties encountered in melting and handling in the molten state magnesium or an alloy largely composed of this metal are well known and these difliculties are still present when it is attempted to introduce such metal into a mold in any process of casting. For example, when using ordinary dry sand mold parts or cores, the casting is'frequently injured on the surface in contact therewith due to burned spots, pitting or similar surface injury. The injury which normally results in the formation of a grayish powder, (presumably an oxide and/or a nitride of the metal) is greatest when the casting poured is of rela tively heavy section. These relatively heavy section castings cool much .slower than thin section castings and accordingly a longer period of time is afforded for the casting to burn, oxidize or be otherwise injured. Even if the impairment of the surface of such.

castings is not serious enough to prevent the cast article from being finished when removed from the mold, the casting has anunsightly appearance and a certain loss of metal is involved. It is to be noted, of course, that the cleaner the casting the more easily may the subsequent finishing operations'be car-' .ried out.

It has heretofore been proposed to over come these difliculties, specifically in casting magnesium and alloys containing the same, by dusting the mold prior to casting the metal, with sulphur or equivalent material capable of giving off in contact with the molten metal a vapor which is more easily oxidizable than magnesium. This procedure, however, has the objection that it is obviously diflicultto correctly gauge the amount of sul- -phur-or equivalent material thus used and particularly ifan excess is applied to the. --surface' of the-mold part at any point so much vapormay be generated that some of Application filed August 30, 1930. Serial No. 479,106.

it becomes entrapped during the period that the metal is solidifying, the result being blowholes or surface shrinks in the casting.

I have now discovered that unexpectedly satisfactory results in the way of producing a casting with a relatively unimpaired surface may be obtained by intermixing with the molding sand before drying or baking one or more protective substances'of the character hereinafter described. The protective substances used should have a boiling or decomposition point appreciably below the casting temperature and abovethe boiling point of water, for example, sulphur, boric acid, and ammonium compounds including ammonium chloride, ammonium sulphate and ammonium bromide; such materials for simplicity will hereinafter be referred to as oxidation inhibitors. mixed with the sand in solid form or may be applied thereto in solution, following which the molding sand, when properly prepared and conditioned, may be molded and the mold then dried or baked so as to be ready for use.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the product hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain means and'modes of carrying out the invention, such disclosed means and modes illustrating, however, but several of the various ways in which the principle of the invention may be used.

The mold parts prepared according to the present invention may be used to form the complete mold or only a part thereof such as a core used for forming ,the inside contour of a piston.

If from of one per cent to 5 per cent by weight of sulphur,'boric acid, ammonium chloride, ammonium sulphate, ammonium bromide, or mixtures of these, be mixed with the molding sand composition before molding and drying or baking, a very satisfactory resalt in the wayof a casting is obtained upon pouring the metal into contact with the so prepared mold part in the u'sualmanner, it

The materials so used may be I being noted, of course, that ordinarily unless Per cent Sulphur 1 to 2 Boric acid 1to 2 Ammonium chloride 2 Ammonium sulphate 2 Ammonium bromide 2 or mixtures of these wherein the sum total percentage of the oxidation inhibitors added is approximately the same as the preferred amount of the individual components. However, I do not wish to be limited to the exact amounts noted above since I have used as high as 10 per cent of such materials with fairly satisfactory results where heavy section castings were concerned. In general, however, the use of such high percentages of the oxidation inhibitors should be avoided since it tends to produce castings injured by blows. In any case the addition agent should be used in very finely divided form or in solution so as to be thoroughly disseminated throughout the sand and avoid any tendency to localized vapor generation during the casting process.

' The following specific examples of molding compositions clearly set. forth in preferred manner the use of my present invention Example 1 (watermoz'stenecl sand) Per cent Molding sand 92 Water, 6

Sulphur 2 -Ewample 2 (oilmoz'stened sand) Parts Sharp sand 60 Oil 1 Dry core binder 1 Sulphur 1 commercial core binders, flour, gluten, etc.

In carrying out the invention the various components of the molding composition including from one to three per cent of oxidation inhibitor, such as sulphur, are thoroughly mixed together and moistenedto the proper molding consistency. The molding composition may then be allowed to stand and temper according to common practice and may thenbe molded to desired form. Following molding, the mold part is dried or baked in conventional manner. The so prepared mold part containing the oxidation inhibitor is then ready for use in casting readily oxidizable metals, although its use is not limited thereto. The preparation of the mold part as described results where the mold part is baked, in a product having the oxidation inhibitor distributed therethrough, the surface thereof, however, normally losing part of its oxidation inhibitor content during the baking step. This loss of oxidation inhibitor from the surface of the mold part I find does not result in any material loss of efficacy of the part during casting and moreover it permits the use of coarser particles of oxidation inhibitor without the danger of excess vaporization thereof with resulting blow-holes or surface shrinks in the casting. After the casting has been, made the molding composition can be reconditioned'for reuse by moistening. and replenishing the oxidation inhibitor driven off during the drying and casting steps.

While I have described my invention in terms of treating sand I do not wish to be limited to that specific material since my invention is broadly applicable to the treatment of mold parts utilizing not only sand but finely divided carbon, finely divided cinders and the like, or combinations of such materials.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the product herein disclosed, provided the product stated by any of the following claims or the equivalent thereof be employed.

I therefore particularly point out and distinctly claim as my invention 1. As an article of manufacture, a molded and dried mold part formed from a molding composition and an ammonium compound.

2. As an article of manufacture, a dry sand mold part consisting of molding sand and from one-half of one per cent to five per cent of an ammonium compound. I

3. As an article of manufacture, a baked sand core consisting of molding sand and from one to three per cent of an ammonium compound.

4. As an article of manufacture, a baked sand mold part consisting of molding sand and approximately two per cent of amnionium chloride.

5. As an article of manufacture, a baked sand mold part containing approximately two per cent of ammonium sulphate.

6. As an article of manufacture, a baked sand mold part containing approximately two per cent of ammonium bromide.

7. As an article of manufacture, a dry sand mold part consisting of sand, 8. core binder, and from one-half of one per cent to five per cent of an ammonium compound.

Signed by me this 27th day of August, 1930.

GEORGE H. WEIDEMANN. 

